Audio based methods and apparatus for detecting a channel change event

ABSTRACT

Methods and apparatus for detecting a channel change event are disclosed. capturing a television audio signal having first, second, and third portions, the first portion occurring earlier in time than the second portion and the second portion occurring earlier in time than the third portion, identifying at least one of a first muted audio condition or a first transient audio condition in the second portion of the television audio signal, and identifying a channel change event in response to: 1) identifying the at least one of the first muted audio condition or the first transient audio condition, 2) failing to identify a second muted audio condition or a second transient audio condition in the first and third portions of the television audio signal, and 3) determining that a time domain length of the second portion of the television audio signal is greater than a first threshold and less than a second threshold.

RELATED APPLICATIONS

This patent arises from a continuation of U.S. patent application Ser.No. 10/570,567, filed Feb. 27, 2006, which is a non-provisionalapplication of PCT Application Ser. No. PCT/US03/27336, filed Aug. 29,2003, the entireties of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure pertains to audience measurement systems and,more particularly, to methods and apparatus for detecting a channelchange event.

BACKGROUND

Determining how many and what type of people are viewing whichtelevision programs helps television program producers improve theirshows and determine a price for advertising slots during those shows. Inaddition, accurate television viewing demographics allow advertisers totarget certain types and sizes of audiences. Similarly, radio listeningdemographics are also useful to producers and advertisers.

To collect these demographics, an audience measurement company, such asNielsen Media Research, may enlist a plurality of television viewers,radio listeners, and/or any other type of audience member. The habits ofthe enlisted audience members are collected to statistically determinethe demographics of the audiences and to develop ratings of thoseprograms. Surveys may be used, but automatic measurement systems arepreferred because of the increased accuracy of the statistics and theconvenience for the viewers.

One aspect of automatic viewer measurement systems is to recordinformation used to determine what television program is showing on atelevision or playing on a radio. Many automatic viewer measurementsystems are non-invasive systems, which do not require installation ofcircuitry within the television or radio. Instead, external devices areused to determine what television program is showing or what radioprogram is playing. In contrast, invasive measurement systems installcircuitry within the information presenting device (e.g., TV, radio,etc.) of the audience member. Invasive techniques are less desirablebecause of the possibility of damage to the information presentationdevice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example television system.

FIG. 2 is a block diagram illustrating an example audio channel changedetector.

FIG. 3 is a block illustrating another example audio channel changedetector.

FIG. 4 is a flowchart representative of machine readable instructionsthat may be executed by a device to implement an example method ofdetecting a television channel change event.

FIG. 5 is a flowchart representative of machine readable instructionsthat may be executed by a device to implement another example method ofdetecting a television channel change event.

FIG. 6 is an example audio signal with a transient during a channelchange event.

FIG. 7 is an example audio signal with a mute during a channel changeevent.

DETAILED DESCRIPTION

Although the following discloses example systems including, among othercomponents, software executed on hardware, it should be noted that suchsystems are merely illustrative and should not be considered aslimiting. For example, it is contemplated that any or all of thedisclosed hardware and software components could be embodied exclusivelyin dedicated hardware, exclusively in software, exclusively in firmwareor in some combination of hardware, firmware and/or software.

In addition, while the following disclosure is made with respect toexample television systems, it should be understood that the disclosedsystem may be used in many other applications. For example, radiosystems may employ the techniques described herein. Accordingly, whilethe following describes example systems and processes, persons ofordinary skill in the art will readily appreciate that the disclosedexamples are not the only way to implement such systems.

In general, the methods and apparatus described herein detect a channelchange event by monitoring an audio signal of an informationpresentation device such as a television system. The monitored audiosignal is tested for certain characteristics indicative of a channelchange event. In some television systems, changing channels produces anaudible “pop” sound or transient. By detecting a normal television audiosignal, followed by a transient television audio signal, followed by anormal television audio signal, the methods and apparatus describedherein can signal when a channel change event has likely occurred.Normal and transient signals are defined using volume level thresholdsand/or frequency thresholds. In other television systems, the “pop”sound produced when changing channels is muted by the television system.In such television systems, channel change events may be detected bydetecting a normal television audio signal, followed by a mutedtelevision audio signal, followed by a normal television audio signal.Muted signals are defined using volume level thresholds and/or frequencythresholds. Once a channel change event is detected, an audiencemeasurement system may automatically determine what program is on theinformation presentation device. Alternatively, an audience member maybe prompted to manually enter what program is on the informationpresentation device.

A block diagram of an example television system 100 is illustrated inFIG. 1. The television system 100 illustrated includes a televisionservice provider 102, a set-top box 104, a signal splitter 106, ananalog-to-digital (A/D) converter 108, a television 110, and an audiochannel change detector 112. The components of the television system 100may be connected as shown.

The television service provider 102 may be any television serviceprovider 102 such as a cable television service provider, a satellitetelevision service provider, and/or a radio frequency (RF) televisionservice provider. The television service provider 102 may provide analogand/or digital television signals. For example, the television serviceprovider 102 may provide analog and/or digital signals over a coaxialcable (e.g., AT&T® cable). Similarly, the television service provider102 may provide analog and/or digital signals over a wirelessconnection, such as a satellite connection (e.g., DIRECTV®) and/or aterrestrial broadcast tower (e.g., “free” TV).

The set-top box 104 may be any set-top box such as a cable televisionconverter, a direct broadcast satellite (DBS) decoder, a digital videorecorder (e.g., TiVo®), a digital video disc (DVD) player, or a videocassette recorder (VCR). The set-top box 104 receives a plurality oftelevision channels from the television service provider 102. Typically,the set-top box 104 selects one of the plurality of television channelsbased on a user input, and outputs an audio/video signal indicative ofthe selected television channel. In the case of an analog signal, theset-top box 104 tunes to a particular frequency to obtain the selectedtelevision channel. In the case of a digital signal, the set-top box 104decodes certain packets of data to obtain the selected televisionchannel. Of course, the set-top box 104 is optional. For example,receiving terrestrial broadcast television may not require a set-top box104.

The output from the set-top box 104 (if included) is fed to a signalsplitter 106 such as a y-splitter. In one example, the signal splitterproduces two signals indicative of the output from the set-top box 104.One of the two signals is fed to the television 110. The other signal isfed to the A/D converter 108. The television 110 may be any type oftelevision. For example, the television may be an NTSC (NationalTelevision Standards Committee) television, a high definition television(HDTV), etc. Of course, a person of ordinary skill in the art willreadily appreciate that any number of signals may be produced by thesignal splitter 106.

The analog-to-digital converter 108 may be any type of analog-to-digitalconverter 108. The analog-to-digital converter 108 converts a standardtelevision audio signal into digital data. For example, theanalog-to-digital converter 108 may convert NTSC audio signals to adigital representation of an audio wave. Alternatively or in addition,the analog-to-digital converter 108 may convert PAL (Phase AlternationLine) audio signals and/or SECAM (Sequential Couleur avec Memoire) audiosignals to digital data. Regardless of the television broadcast standardconverted, the digital data may be any size and may encode any number ofdata points. Alternatively, an analog sampling device may be usedinstead of the A/D converter 108.

The analog-to-digital converter 108 periodically (e.g., at 200 MHz)takes a sample and passes the digital data representing the televisionaudio to the audio channel change detector 112. The audio channel changedetector 112 scans the digital data it receives to determine if channelchange events are occurring.

A block diagram of an example audio channel change detector 112 isillustrated in FIG. 2. The channel change detector 112 may be a personalcomputer (PC), an application specific device, and/or any othercomputing device. In an example, the channel change detector 112includes a main processing unit 202 powered by a power supply 203. Themain processing unit 202 may include a processor 204 electricallycoupled by a system interconnect 206 to a main memory device 208 and oneor more interface circuits 210. In an example, the system interconnect206 is an address/data bus. Of course, a person of ordinary skill in theart will readily appreciate that interconnects other than busses may beused to connect the processor 204 to the main memory device 208. Forexample, one or more dedicated lines and/or a crossbar may be used toconnect the processor 204 to the main memory device 208.

The processor 204 may include any type of well known central processingunit (CPU), such as a microprocessor from the Intel Pentium® family ofmicroprocessors, the Intel Itanium° family of microprocessors, and/orthe Intel XScale® family of processors. The processor 204 may includeany type of well known cache memory, such as static random access memory(SRAM). The main memory device 208 may include dynamic random accessmemory (DRAM), but may also include non-volatile memory. In an example,the main memory device 208 stores a software program which is executedby processor 204 in a well known manner.

The interface circuit(s) 210 may be implemented using any type of wellknown interface standard, such as an analog cable interface, a digitalcable interface, a satellite signal interface, an Ethernet interface,and/or a Universal Serial Bus (USB) interface. One or more input devices212 may be connected to the interface circuits 210 for entering data andcommands into the main processing unit 202. For example, an input device212 may be a keyboard, mouse, touch screen, track pad, track ball,isopoint, and/or a voice recognition system. In addition, the interfacecircuit(s) 210 handle digital data inputs from the analog-to-digitalconverter 108. In an example, the analog-to-digital converter 108 isincorporated into the channel change detector 112.

One or more displays, printers, speakers, and/or other output devices214 may also be connected to the main processing unit 202 via one ormore of the interface circuits 210. The display 214 may be cathode raytube (CRTs), liquid crystal displays (LCDs), or any other type ofdisplay. The display 214 may generate visual indications of datagenerated during operation of the main processing unit 202. The visualdisplays may include prompts for human operator input, calculatedvalues, detected data, etc.

The channel change detector 112 may also include one or more storagedevices 216. For example, the channel change detector 112 may includeone or more hard drives, a compact disk (CD) drive, a digital versatiledisk drive (DVD), and/or other computer media input/output (I/O)devices.

The channel change detector 112 may also exchange data with otherdevices via a connection to a network 218. The network connection may beany type of network connection, such as an Ethernet connection, digitalsubscriber line (DSL), telephone line, coaxial cable, etc. The network218 may be any type of network, such as the Internet, a telephonenetwork, a cable network, and/or a wireless network.

A block diagram of another example audio channel change detector 112 isillustrated in FIG. 3. In this example, the channel change detector 112includes a sampler 302, a timer 304, a threshold detector 306, a buffer308, and a state machine 310 interconnected as shown. The audio channelchange detector 112 of FIG. 3 may be implemented using hardware and/orsoftware, such as dedicated circuits and/or processor(s) executinginstructions.

In operation, the sampler 302 periodically captures a portion of theaudio signal from the television system 100. The sampler 302 may be anytype of sampler. For example, the sampler may an analog-to-digitalconverter. In such an event, the analog-to-digital converter 108 is notrequired. In another example, the sampler 302 may be a voltage and/orfrequency measurement circuit. The frequency at which the sampler 302captures portions of the audio signal is based on a signal from thetimer 304. The timer may be any type of timer such as a crystaloscillator or a resonator.

In this example, the output of the sampler 302 is passed to thethreshold detector 306. The output of the sampler 302 may be digital oranalog. The threshold detector 306 compares the output of the sampler302 to one or more predetermined thresholds. The threshold detector 306may logically compare digital data indicative of the audio signal to oneor more predetermined digital thresholds. Alternatively, the thresholddetector 306 may compare one or more analog voltage levels indicative ofthe audio signal to a one or more predetermined voltage thresholds. Forexample, the threshold detector may be a digital comparator, an analogcomparator, or a processor executing one or more comparisoninstructions.

Each time the threshold detector 306 makes a comparison of the audiosignal to the predetermined thresholds, the threshold detector 306outputs a signal to the buffer 308. The signal indicates if the audiosignal is greater than or less than a predetermined threshold. Thebuffer 308 stores data indicative of the series of signals coming formthe threshold detector 306. The buffer 308 may be any type of buffersuch as a shift register or an addressable memory.

Data stored in the buffer 308 is then passed to the state machine 310.The state machine 310 determines if a channel change event has occurredbased on the sequence of threshold crossings reported by the audiochannel change detector 112. The state machine 310 may be implementedusing any type of circuitry. For example, the state machine 310 may be alogic circuit or a processor executing instructions as described below.When the state machine 310 detects a channel change event, the statemachine 310 outputs a signal indicative of the channel change event. Forexample, the signal may be a voltage level or a pulse.

An example process 400 for detecting a television channel change eventis illustrated in FIG. 4. Preferably, the process 400 is embodied in oneor more software programs that are stored in one or more memories andexecuted by one or more processors (e.g., processor 204) in a well knownmanner. However, some or all of the blocks of the process 400 may beperformed manually and/or by another hardware device. For example, theprocess 400 may be executed by the audio channel change detector 112 ofFIG. 2 and/or the audio channel change detector 112 of FIG. 3. Althoughthe process 400 is described with reference to the flowchart illustratedin FIG. 4, a person of ordinary skill in the art will readily appreciatethat many other methods of performing the process 400 may be used. Forexample, the order of many of the blocks may be altered, the operationof one or more blocks may be changed, blocks may be combined, and/orblocks may be eliminated.

In general, the example process 400 detects a television channel changeevent by monitoring an audio signal of a television system 100. Themonitored audio signal is tested for certain characteristics indicativeof a channel change event. In some television systems 100, changingchannels produces an audible “pop” sound or transient. By detecting anormal television audio signal, followed by a transient television audiosignal, followed by a normal television audio signal, the methods andapparatus described herein can signal when a channel change event haslikely occurred. Normal and transient signals are defined using volumelevel thresholds and/or frequency thresholds as described below. Anexample audio signal with a transient during a channel change event isillustrated in FIG. 6.

The example process 400 begins when the audio channel change detector112 initializes a plurality of variables (block 402). The variables maybe initialized based on a type of television equipment (e.g., a brand).For example, a variables “A”, “B”, and “C” may be initialized. Variable“A” may represent the number of samples (e.g., 60) of a group of samples(e.g., 100) that must be below a threshold (e.g., a volume level) duringa first state in order to advance the process 400 to a second state.Variable “B” may represent the number of samples (e.g., 90) of a groupof samples (e.g., 100) that must be above a threshold (e.g., a volumelevel) during the second state in order to advance the process 400 to athird state. Variable “C” may represent the number of samples (e.g., 60)of a group of samples (e.g., 100) that must be below a threshold (e.g.,a volume level) during the third state in order to indicate that achannel change event occurred. Of course the values used herein aremerely examples, and many other variables may be initialized. Inaddition, these variables may be dynamically updated. For example,transient audio signals may be identified by detecting energy peaksrelative to a substantially stationary signal. In other words, thevolume levels described herein may be relative volume levels, notabsolute volume levels.

After initialization (block 402), the process 400 starts in a firststate (block 404). In the first state, the process 400 looks for certainpre-channel change conditions. For example, the process 400 may look fornormal audio signals, which may be characterized by one or morepredetermined volume level thresholds and/or predetermined frequencythresholds. In one example, a predetermined number of audio signalsamples being less than a predetermined threshold is indicative of a“normal” audio signal.

Accordingly, the process 400 periodically samples the audio signal(block 406). For example, the process 400 may take 100 samples that are50 milliseconds (ms) apart. As described above, the samples may beanalog samples and/or digital samples. Once a plurality of audio samplesare taken (or after every sample), the example process 400 checks if acertain number of the audio samples are below a predetermined threshold(block 408). For example, the process 400 may determine if 60 out of 100samples are below a certain volume level threshold. The threshold volumelevel may be a moving average threshold plus a margin constant (i.e., aband slightly above a historical average associated with the audiosignal). If a sufficient number of the audio signal samples are notbelow the threshold, the example process 400 stays in the first state(block 404) and takes additional samples of the audio signal (block406). If a sufficient number of the audio signal samples are below thethreshold (i.e., normal audio is occurring), the example process 400advances to a second state (block 410).

In the second state, the example process 400 looks for a transientcondition (block 410). The transient condition may be characterized byone or more predetermined volume level thresholds and/or predeterminedfrequency thresholds. In one example, a transient audio signal isdetected by finding a predetermined number of audio signal samples abovea predetermined threshold for a predetermined time period. An exampleaudio signal with a transient during a channel change event isillustrated in FIG. 6.

Accordingly, in the second state, the process 400 periodically samplesthe audio signal (block 412). For example, the process 400 may take 100samples that are 50 milliseconds (ms) apart. Again, the samples may beanalog samples and/or digital samples. Once a plurality of audio samplesare taken (or after every sample), the example process 400 checks if acertain number of the audio samples are above a predetermined threshold(block 414). For example, the process 400 may determine if 30 out of 100samples are above a certain volume level threshold. Again, the thresholdvolume level may be a moving average threshold plus a margin constant(i.e., a band slightly above a historical average associated with theaudio signal). If a sufficient number of the audio signal samples arenot above the threshold, the example process 400 reverts back to thefirst state (block 404) and takes additional samples of the audio signal(block 406). However, if a sufficient number of the audio signal samplesare above the threshold (e.g., a transient spike occurred), the exampleprocess 400 advances to a third state (block 416).

In the third state, the process 400 looks for certain post-channelchange conditions. For example, the process 400 may look for normalaudio signals again. Accordingly, the process 400 periodically samplesthe audio signal (block 418). Once a plurality of audio samples aretaken (or after every sample), the example process 400 determines if acertain number of the audio samples are below a predetermined threshold(block 420). For example, the process 400 may determine if 60 out of 100samples are below a certain volume level threshold. If a sufficientnumber of the audio signal samples are not below the threshold, theexample process 400 reverts back to the first state (block 404) andtakes additional samples of the audio signal (block 406). However, if asufficient number of the audio signal samples are below the threshold(i.e., normal audio is occurring again), the example process 400indicates a channel change event has occurred (block 422). Subsequently,the process 400 may repeat in order to detect additional channel changeevents.

Another example process 500 for detecting a television channel changeevent is illustrated in FIG. 5. Preferably, the process 500 is embodiedin one or more software programs that are stored in one or more memoriesand executed by one or more processors (e.g., processor 204) in a wellknown manner. However, some or all of the blocks of the process 500 maybe performed manually and/or by another hardware device. For example,the process 500 may be executed by the audio channel change detector 112of FIG. 2 and/or the audio channel change detector 112 of FIG. 3.Although the process 500 is described with reference to the flowchartillustrated in FIG. 5, a person of ordinary skill in the art willreadily appreciate that many other methods of performing the process 500may be used. For example, the order of many of the blocks may bealtered, the operation of one or more blocks may be changed, blocks maybe combined, and/or blocks may be eliminated.

In general, the example process 500 detects a television channel changeevent by monitoring an audio signal of a television system 100. Themonitored audio signal is tested for certain characteristics indicativeof a channel change event. In some television systems 100, the “pop”sound produced by changing channels is muted by the television system100. In such television systems 100, channel change events may bedetected by detecting a normal television audio signal, followed by amuted television audio signal, followed by a normal television audiosignal. Normal and muted signals are defined using volume levelthresholds and/or frequency thresholds as described below. An exampleaudio signal with a mute during a channel change event is illustrated inFIG. 7.

The example process 500 begins when the audio channel change detector112 initializes a plurality of variables (block 502). These variablesmay be initialized based on a type of television equipment (e.g., abrand). For example, variables “A”, “B”, “C” and “X” may be initialized.Variable “A” may represent the number of samples (e.g., 60) of a groupof samples (e.g., 100) that must be above a threshold (e.g., a volumelevel) during a first state in order to advance the process 400 to asecond state. Variable “B” may represent the number of samples (e.g.,90) of a group of samples (e.g., 100) that must be below a threshold(e.g., a volume level) during the second state in order to advance theprocess 400 to a third state. Variable “C” may represent the number ofsamples (e.g., 60) of a group of samples (e.g., 100) that must be abovea threshold (e.g., a volume level) during the third state in order toindicate that a channel change event occurred. Variable “X” mayrepresent a time period (e.g., 15 seconds) after which a muted conditionis treated as a television off condition or a “user mute” condition. Ofcourse the values used herein are merely examples, and many othervariables may be initialized. In addition, these variables may bedynamically updated. For example, muted audio signals may be identifiedby detecting energy lows relative to a substantially stationary signal.In other words, the volume levels described herein may be relativevolume levels, not absolute volume levels.

After initialization (block 502), the process 500 starts in a firststate (block 504). In the first state, the process 500 looks for certainpre-channel change conditions. For example, the process 500 may look fornormal audio signals. Normal audio signals may be characterized by oneor more predetermined volume level thresholds and/or predeterminedfrequency thresholds. In one example, a predetermined number of audiosignal samples being less than a predetermined threshold is indicativeof a “normal” audio signal.

Accordingly, the process 500 periodically samples the audio signal(block 506). For example, the process 500 may take 100 samples that are50 milliseconds (ms) apart. As described above, the samples may beanalog samples and/or digital samples. Once a plurality of audio samplesare taken (or after every sample), the example process 500 checks if acertain number of the audio samples are above a predetermined threshold(block 508). For example, the process 500 may determine if 60 out of 100samples are above a certain volume level threshold. The threshold volumelevel may be a moving average threshold minus a margin constant (i.e., aband slightly below historically averaged audio signals). If asufficient number of the audio signal samples are not above thethreshold, the example process 500 stays in the first state (block 504)and takes additional samples of the audio signal (block 506). If asufficient number of the audio signal samples are above the threshold(i.e., normal audio is occurring), the example process 500 advances to asecond state (block 410).

In the second state, the example process 500 looks for a muted condition(block 510). The muted condition may be characterized by one or morepredetermined volume level thresholds and/or predetermined frequencythresholds. In one example, a muted audio signal is detected by findinga predetermined number of audio signal samples below a predeterminedthreshold for a predetermined time period. An example audio signal witha mute during a channel change event is illustrated in FIG. 7.

Accordingly, the process 500 periodically samples the audio signal(block 512) and checks if a certain number of the audio samples arebelow a predetermined threshold (block 514). Again, the threshold volumelevel may be a band slightly below historically averaged audio signals.If a sufficient number of the audio signal samples are not below thethreshold, the example process 500 reverts back to the first state(block 504) and takes additional samples of the audio signal (block506). However, if a sufficient number of the audio signal samples arebelow the threshold (i.e., a mute occurred), the example process 500checks if the muted condition has lasted longer than a predeterminedamount of time (block 516). If the muted condition has lasted longerthan a predetermined amount of time, the process 500 reverts back to thefirst state (block 504). For example, if a muted condition exists for 30minutes, the example process 500 may assume the television has beenturned off In another example, if the muted condition lasts 15 seconds,it may be assumed that the viewer intentionally muted the televisionrather than the muting having been caused by a channel change event. Ifa sufficient number of the audio signal samples are below the threshold(i.e., a mute occurred), and the muted condition has not lasted longerthan a predetermined amount of time (e.g., the television is notintentionally muted or turned off), the process 500 advances to a thirdstate (block 518).

In the third state, the process 500 looks for certain post-channelchange conditions. For example, the process 500 may look for normalaudio signals again. Accordingly, the process 500 periodically samplesthe audio signal (block 520) and checks if a certain number of the audiosamples are above a predetermined threshold (block 522). If a sufficientnumber of the audio signal samples are not above the threshold, theexample process 500 reverts back to block 514 to determine if audio isstill muted. If the audio is still muted, the process 500 determines ifthe mute condition has lasted long enough to assume the television hasbeen turned off (block 516). However, if a sufficient number of theaudio signal samples are above the threshold (i.e., normal audio isoccurring again), the example process 500 indicates a channel changeevent has occurred (block 524).

In addition to each of the separate processes 400 and 500, a person ofordinary skill in the art will readily appreciate that process 400 andprocess 500 may be combined. For example, when looking for normal audio,the combined process may look for volume levels that are both (i) abovea first predetermined threshold like process 400 and (ii) below a secondpredetermined threshold like process 500. Similarly, the combinedprocess may accept either a transient condition or a muted condition assatisfying the conditions of the second state.

An example audio signal 600 generated during a channel change event isillustrated in FIG. 6. In this example, a transient signal 602 isgenerated during the channel change event. The portion 604 of the audiowhich occurs before the transient 602 is normal or stationary audiobecause a certain percentage (e.g., >80%) of the audio before thechannel change has a volume (or energy) level below a threshold 606. Thethreshold may be a moving average plus some constant 608 (i.e., ahorizontal line slightly above an average peak line 610). Similarly, theportion 612 of the audio which occurs after the transient 602 is“normal” or “stationary” audio because a certain percentage (e.g., >80%)of the audio after the channel change also has a volume (or energy)level below the threshold 606.

In the portion 604 of the audio before the channel change, some of theaudio peaks 614 may go above the threshold 606, but most of the audiopeaks 616 fall below the threshold 606. Similarly, in the portion 612 ofthe audio after the channel change, most of the audio peaks 618 fallbelow the threshold 606. Conversely, in the portion 602 of the audioduring the channel change, some of the audio peaks 620 may fall belowthe threshold 606, but most of the audio peaks 622 reach above thethreshold 606.

Another example audio signal 700 generated during a channel change eventis illustrated in FIG. 7. In this example, a mute signal 702 isgenerated during the channel change event. The portion 704 of the audiowhich occurs before the mute 702 is normal or stationary audio because acertain percentage (e.g., >80%) of the audio before the channel changehas a volume (or energy) level above a threshold 706. The threshold maybe a moving average plus some constant 708 (i.e., a horizontal lineslightly below an average peak line 710). Similarly, the portion 712 ofthe audio which occurs after the mute 702 is normal or stationary audiobecause a certain percentage (e.g., >80%) of the audio after the channelchange also has a volume (or energy) level above the threshold 706.

In the portion 704 of the audio before the channel change, some of theaudio peaks 714 may fall below the threshold 706, but most of the audiopeaks 716 go above the threshold 706. Similarly, in the portion 712 ofthe audio after the channel change, most of the audio peaks 718 reachabove the threshold 706, even though some peaks 720 may fall below thethreshold 706. In the example illustrated in FIG. 7, the portion 702 ofthe audio that is muted falls entirely below the threshold 706. However,a person of ordinary skill in the art will readily appreciate that theportion 702 of the audio that is muted need not fall entirely below thethreshold 706.

Although certain apparatus have been described herein, the scope ofcoverage of this patent is not limited thereto. On the contrary, thispatent covers all apparatuses, methods and articles of manufacturefairly falling within the scope of the appended claims either literallyor under the doctrine of equivalents.

1. A method of detecting a channel change event, the method comprising:capturing a television audio signal having first, second, and thirdportions, the first portion occurring earlier in time than the secondportion and the second portion occurring earlier in time than the thirdportion; identifying at least one of a first muted audio condition or afirst transient audio condition in the second portion of the televisionaudio signal; and identifying, using a processor, a channel change eventin response to: 1) identifying the at least one of the first muted audiocondition or the first transient audio condition; 2) failing to identifya second muted audio condition or a second transient audio condition inthe first and third portions of the television audio signal; and 3)determining that a time domain length of the second portion of thetelevision audio signal is greater than a first threshold and less thana second threshold.
 2. A method as defined in claim 1, furthercomprising determining an audio threshold level based on the capturedtelevision audio signal.
 3. A method as defined in claim 2, whereinidentifying the muted audio condition comprises comparing a number ofaudio samples of the second portion of the television audio signal thatare less than the audio threshold level to a sample threshold.
 4. Amethod as defined in claim 2, wherein identifying the transient audiocondition comprises comparing a number of audio samples of the secondportion of the television audio signal that are greater than the audiothreshold level to a sample threshold.
 5. A method as defined in claim2, wherein failing to identify the second muted audio condition in thefirst and third portions of the television audio signal comprisesdetermining that the first and third portions of the television audiosignal have at least a threshold number of audio samples greater thanthe audio threshold level.
 6. A method as defined in claim 2, whereinfailing to identify the second transient audio condition in the firstand third portions of the television audio signal comprises determiningthat the first and third portions of the television audio signal have atleast a threshold number of audio samples less than the audio thresholdlevel.
 7. A method as defined in claim 1, further comprising sending achannel change detection signal to an audience measurement device.
 8. Anapparatus to detect a television channel change event, comprising: aninput device to receive a television audio signal; a memory to storedigital data representative of a first portion, a second portion, and athird portion of the television audio signal; and a processor programmedto identify at least one of a first muted audio condition or a firsttransient audio condition in the second portion of the television audiosignal, and to identify a channel change event in response to: 1)identifying the first muted audio condition or the first transient audiocondition; 2) failing to identify a second muted audio condition or asecond transient audio condition in the first and third portions of thetelevision audio signal; and 3) determining that a time domain length ofthe second portion of the television audio signal is greater than afirst threshold and less than a second threshold.
 9. An apparatus asdefined in claim 8, wherein the processor is to determine an audiothreshold level based on a volume level of the television audio signal.10. An apparatus as defined in claim 9, wherein the audio thresholdlevel is a combination of an average peak volume level of the televisionaudio signal and a constant.
 11. An apparatus as defined in claim 8,wherein the processor is to identify the at least one of the first mutedaudio condition or the first transient audio condition in the secondportion of the television audio signal.
 12. An apparatus as defined inclaim 11, wherein the processor is to determine whether at least one ofthe second muted audio condition or the second transient audio conditionexists in at least one of the first or third portions of the televisionaudio signal.
 13. An apparatus as defined in claim 8, wherein theprocessor is to output a channel change detection signal to an audiencemeasurement device in response to identifying a channel change event.14. A tangible article of manufacture comprising machine readableinstructions which, when executed, cause a machine to at least: capturea television audio signal having first, second, and third portions, thefirst portion occurring earlier in time than the second portion and thesecond portion occurring earlier in time than the third portion;identify at least one of a first muted audio condition or a firsttransient audio condition in the second portion of the television audiosignal; and identify a channel change event in response to: 1)identifying the at least one of the first muted audio condition or thefirst transient audio condition; 2) failing to identify a second mutedaudio condition or a second transient audio condition in the first andthird portions of the television audio signal; and 3) determining that atime domain length of the second portion of the television audio signalis greater than a first threshold and less than a second threshold. 15.An article of manufacture as defined in claim 14, wherein theinstructions cause the machine to determine an audio threshold levelbased on the captured television audio signal.
 16. An article ofmanufacture as defined in claim 15, wherein identifying the muted audiocondition comprises comparing a number of audio samples of the secondportion of the television audio signal that are less than the audiothreshold level to a sample threshold.
 17. An article of manufacture asdefined in claim 15, wherein identifying the transient audio conditioncomprises comparing a number of audio samples of the second portion ofthe television audio signal that are greater than the audio thresholdlevel to a sample threshold.
 18. An article of manufacture as defined inclaim 15, wherein failing to identify the second muted audio conditionin the first and third portions of the television audio signal comprisesdetermining that the first and third portions of the television audiosignal have at least a threshold number of audio samples greater thanthe audio threshold level.
 19. An article of manufacture as defined inclaim 15, wherein failing to identify the second transient audiocondition in the first and third portions of the television audio signalcomprises determining that the first and third portions of thetelevision audio signal have at least a threshold number of audiosamples less than the audio threshold level.
 20. An article ofmanufacture as defined in claim 14, wherein the instructions cause themachine to send a channel change detection signal to an audiencemeasurement device.